LTC1485
Differential Bus Transceiver
FEATURES
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
ESD Protection over
±
10kV
Low Power: I
CC
= 1.8mA Typ
28ns Typical Driver Propagation Delays with
4ns Skew
Designed for RS485 or RS422 Applications
Single 5V Supply
– 7V to 12V Bus Common-Mode Range Permits
±7V
Ground Difference Between Devices on the Bus
Thermal Shutdown Protection
Power-Up/Down Glitch-Free Driver Outputs
Driver Maintains High Impedance in Three-State or
with the Power Off
Combined Impedance of a Driver Output and
Receiver Allows up to 32 Transceivers on the Bus
60mV Typical Input Hysteresis
Pin Compatible with the SN75176A, DS75176A, and
SN75LBC176
The LTC
®
1485 is a low power differential bus/line trans-
ceiver designed for multipoint data transmission standard
RS485 applications with extended common-mode range
(12V to – 7V). It also meets the requirements of RS422.
The CMOS with Schottky design offers significant power
savings over its bipolar counterpart without sacrificing
ruggedness against overload or ESD damage.
The driver and receiver feature three-state outputs, with
the driver outputs maintaining high impedance over the
entire common-mode range. Excessive power dissipation
caused by bus contention or faults is prevented by a
thermal shutdown circuit which forces the driver outputs
into a high impedance state. I/O pins are protected against
multiple ESD strikes of over
±10kV.
The receiver has a fail-safe feature which guarantees a
high output state when the inputs are left open.
Both AC and DC specifications are guaranteed from – 40°C
to 85°C and 4.75V to 5.25V supply voltage range.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATI
s
s
S
Low Power RS485/RS422 Transceiver
Level Translator
TYPICAL APPLICATI
DE
3
5V
8
LTC1485
6
6
120Ω
7
5V
8
LTC1485
DI
4
DRIVER
120Ω
7
4000 FT 24 GAUGE TWISTED PAIR
RO
1
RECEIVER
2
RE
5
5
U
DE
3
DRIVER
4
DI
RECEIVER
1
RO
2
RE
1485 TA01
UO
UO
1
LTC1485
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RO 1
RE 2
DE 3
DI 4
D
R
8 V
CC
7 B
6
A
Supply Voltage (V
CC
) .............................................. 12V
Control Input Voltages ................... – 0.5V to V
CC
+ 0.5V
Control Input Currents ........................ – 50mA to 50mA
Driver Input Voltages ..................... – 0.5V to V
CC
+ 0.5V
Driver Input Currents .......................... – 25mA to 25mA
Driver Output Voltages .........................................
±14V
Receiver Input Voltages ........................................
±14V
Receiver Output Voltages .............. – 0.5V to V
CC
+ 0.5V
Operating Temperature Range
LTC1485C .............................................. 0°C to 70°C
LTC1485I .......................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
ORDER PART
NUMBER
LTC1485CN8
LTC1485IN8
LTC1485CS8
LTC1485IS8
S8 PART MARKING
1485
1485I
5 GND
S8 PACKAGE
N8 PACKAGE
8-LEAD PLASTIC DIP 8-LEAD PLASTIC SOIC
T
JMAX
= 125°C,
θ
JA
= 100°C/ W (N)
T
JMAX
= 150°C,
θ
JA
= 150°C/ W (S)
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
V
CC
= 5V (Notes 2, 3), unless otherwise noted.
SYMBOL
V
OD1
V
OD2
∆V
OD
V
OC
∆|
V
OC
|
V
INH
V
INL
I
IN1
I
IN2
V
TH
∆V
TH
V
OH
V
OL
I
OZR
I
CC
PARAMETER
Differential Driver Output Voltage (Unloaded)
Differential Driver Output Voltage (With Load)
Change in Magnitude of Driver Differential
Output Voltage for Complementary Output States
Driver Common-Mode Output Voltage
Change in Magnitude of Driver Common-Mode
Output Voltage for Complementary Output States
Input High Voltage
Input Low Voltage
Input Current
Input Current (A, B)
Differential Input Threshold Voltage for Receiver
Receiver Input Hysteresis
Receiver Output High Voltage
Receiver Output Low Voltage
Three-State Output Current at Receiver
Supply Current
CONDITIONS
I
O
= 0
R = 50Ω, (RS422)
R = 27Ω, (RS485) (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
R = 27Ω or R = 50Ω (Figure 1)
DI, DE, RE
DI, DE, RE
DI, DE, RE
V
CC
= 0V or 5.25V, V
IN
= 12V
V
CC
= 0V or 5.25V, V
IN
= – 7V
– 7V
≤
V
CM
≤
12V
V
CM
= 0V
I
O
= – 4mA, V
ID
= 0.2V
I
O
= 4mA, V
ID
= – 0.2V
V
CC
= Max 0.4V
≤
V
O
≤
2.4V
No Load; DI = GND or V
CC
Outputs Enabled
Outputs Disabled
– 7V
≤
V
CM
≤
12V
V
O
= – 7V
V
O
= 10 V
0V
≤
V
O
≤
V
CC
MIN
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
TYP
5
MAX
V
5
0.2
3
0.2
UNITS
V
V
V
V
V
V
V
µA
mA
mA
V
mV
V
V
µA
mA
mA
kΩ
mA
mA
mA
2
1.5
2.0
0.8
±2
1.0
– 0.8
0.2
60
3.5
0.4
±1
1.8
1.7
12
250
250
85
2.3
2.3
– 0.2
R
IN
I
OSD1
I
OSD2
I
OSR
Receiver Input Resistance
Driver Short-Circuit Current, V
OUT
= High
Driver Short-Circuit Current, V
OUT
= Low
Receiver Short-Circuit Current
7
2
U
W
U
U
W W
W
LTC1485
SWITCHI G CHARACTERISTICS
V
CC
= 5V (Notes 2, 3), unless otherwise noted.
SYMBOL
t
PLH
t
PHL
t
SKEW
t
r
, t
f
t
ZH
t
ZL
t
LZ
t
HZ
t
PLH
t
PHL
t
SKEW
t
ZL
t
ZH
t
LZ
t
HZ
PARAMETER
Driver Input to Output
Driver Input to Output
Driver Output to Output
Driver Rise or Fall Time
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
Receiver Input to Output
Receiver Input to Output
| t
PLH
– t
PHL
|
Differential Receiver Skew
Receiver Enable to Output Low
Receiver Enable to Output High
Receiver Disable from Low
Receiver Disable from High
CONDITIONS
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 5)
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 5)
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 5)
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF
(Figures 2, 5)
C
L
= 100pF (Figures 4, 6) S2 Closed
C
L
= 100pF (Figures 4, 6) S1 Closed
C
L
= 15pF (Figures 4, 6) S1 Closed
C
L
= 15pF (Figures 4, 6) S2 Closed
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF (Figures 2, 7)
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF (Figures 2, 7)
R
DIFF
= 54Ω, C
L1
= C
L2
= 100pF (Figures 2, 7)
C
L
= 15pF (Figures 3, 8) S1 Closed
C
L
= 15pF (Figures 3, 8) S2 Closed
C
L
= 15pF (Figures 3, 8) S1 Closed
C
L
= 15pF (Figures 3, 8) S2 Closed
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
The
q
denotes specifications which apply over the operating temperature
range.
Note 1:
Absolute Maximum Ratings are those values beyond which the
safety of the device cannot be guaranteed.
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Output Low Voltage vs
Output Current
36
32
T
A
= 25°C
–18
–16
T
A
= 25°C
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
28
24
20
16
12
8
4
0
0
0.5
1.5
1.0
OUTPUT VOLTAGE (V)
2.0
1485 G01
OUTPUT VOLTAGE (V)
U W
U
MIN
10
10
TYP
30
30
4
MAX
50
50
10
25
70
70
70
70
50
55
15
45
45
45
45
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
5
15
40
40
40
40
25
30
5
30
30
30
30
15
20
Note 2:
All currents into device pins are positive. All currents out of device
pins are negative. All voltages are referenced to device ground unless
otherwise specified.
Note 3:
All typicals are given for V
CC
= 5V and T
A
= 25°C.
Receiver Output High Voltage vs
Output Current
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
5
4
3
OUTPUT VOLTAGE (V)
1485 G02
Receiver Output High Voltage vs
Temperature
I = 8mA
–14
–12
–10
–8
–6
–4
–2
0
2
3.0
–50
–25
0
75
50
25
TEMPERATURE (°C)
100
125
1485 G03
3
LTC1485
TYPICAL PERFOR A CE CHARACTERISTICS
Receiver Output Low Voltage
vs Temperature
0.9
0.8
0.7
OUTPUT VOLTAGE (V)
I = 8mA
OUTPUT CURRENT (mA)
0.6
0.5
0.4
0.3
0.2
0.1
0
–50
48
DIFFERENTIAL VOLTAGE (V)
–25
0
75
50
25
TEMPERATURE (°C)
Driver Output Low Voltage vs
Output Current
80
OUTPUT CURRENT (mA)
T
A
= 25°C
OUTPUT CURRENT (mA)
60
–72
INPUT THRESHOLD VOLTAGE (V)
40
20
0
0
1
3
2
OUTPUT VOLTAGE (V)
4
1485 G07
Receiver | t
PLH
– t
PHL
| vs
Temperature
5
5
4
4
SUPPLY CURRENT (mA)
TIME (ns)
TIME (ns)
3
2
1
–50
–25
0
75
25
50
TEMPERATURE (°C)
4
U W
100
1485 G04
Driver Differential Output Voltage
vs Output Current
64
T
A
= 25°C
2.4
Driver Differential Output Voltage
vs Temperature
R
L
=54Ω
2.2
32
2.0
16
1.8
0
125
0
1
3
2
OUTPUT VOLTAGE (V)
4
1485 G05
1.6
–50
–25
0
75
25
50
TEMPERATURE (°C)
100
125
1485 G06
Driver Output High Voltage vs
Output Current
–96
T
A
= 25°C
1.63
TTL Input Threshold vs
Temperature
1.61
–48
1.59
–24
1.57
0
0
1
3
2
OUTPUT VOLTAGE (V)
4
1485 G08
1.55
–50
–25
0
75
50
25
TEMPERATURE (°C)
100
125
1485 G09
Driver Skew vs Temperature
1.8
Supply Current vs Temperature
DRIVER ENABLED
1.7
3
1.6
DRIVER DISABLED
1.5
2
100
125
1
–50
–25
0
75
25
50
TEMPERATURE (°C)
100
125
1.4
–50
–25
0
75
25
50
TEMPERATURE (°C)
100
125
1485 G10
1485 G11
1485 G12
LTC1485
PI FU CTIO S
RO (Pin 1):
Receiver Output. If the receiver output is
enabled (RE low), then if A > B by 200mV, RO will be high.
If A < B by 200mV, then RO will be low.
RE (Pin 2):
Receiver Output Enable. A low enables the
receiver output, RO. A high input forces the receiver
output into a high impedance state.
DE (Pin 3):
Driver Output Enable. A high on DE enables the
driver outputs, A and B. A low input will force the driver
outputs into a high impedance state.
DI (Pin 4):
Driver Input. If the driver outputs are enabled
(DE high), then a low on DI forces the driver outputs A low
and B high. A high on DI will force A high and B low.
GND (Pin 5):
Ground Connection.
A (Pin 6):
Driver Output/Receiver Input.
B (Pin 7):
Driver Output/Receiver Input.
V
CC
(Pin 8):
Positive Supply. 4.75V
≤
V
CC
≤
5.25V.
TEST CIRCUITS
A
R
V
OD2
R
B
V
OC
Figure 1. Driver DC Test Load
RECEIVER
OUTPUT
C
L
1k
S2
Figure 3. Receiver Timing Test Load
U
U
U
A
DI
DRIVER
B
R
DIFF
C
L1
A
RECEIVER
RO
15pF
C
L2
B
1485 F02
1485 F01
Figure 2. Driver/Receiver Timing Test Circuit
S1
1k
V
CC
S1
V
CC
OUTPUT
UNDER TEST
500Ω
C
L
1485 F03
S2
1485 F04
Figure 4. Driver Timing Test Load
5
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